The present invention relates generally to transducers for sensing vibrations. More particularly, a multicomponent transducer has been developed employing a single inertial mass to sense one or more components of seismic disturbances in the earth and to generate signals representative of the magnitude and periodicity thereof.
In seismic reflection and refraction investigations, exploration geophysicists and earth seismologists have used transducers to sense the earth's response to seismic energy generated by seismic sources (e.g., explosives, vibrators, impulsive sources, etc.) as well as seismic energy generated by natural phenomena (e.g., earthquakes). Such transducers comprise geophones and seismometers having sensing elements which have been generally constrained to linear motion. Typically, such sensing elements include a single spring-mounted inertial mass ideally constrained to linear motion along a selected axis. However, such sensing elements cannot truly be constrained to linear motion along the selected axis. Rather, the motion of the inertial mass can be affected by motion along axes other than that prescribed. Consequently, signals generated by such transducers (which are intended to be representative of the motion of the inertial mass along the constrained axis only) can be contaminated by signal components due to motions along other axes and can thus be misleading.
Alternative transducers have been described by Russell, et al., in U.S. Pat. No. 4,047,439; by Hunter, et al., in U.S. Pat. No. 4,043,204; by Lister in Canadian Pat. No. 1,229,406; and by Rosensweig in U.S. Pat. No. 3,488,531. Such transducers all employ a ferrohydrodynamically levitated single inertial mass generally constrained to linear motion along a selected axis. These levitated inertial mass transducers suffer from the same shortcomings of the spring-mounted masses sensing systems, i.e., each attempts to develop signals representative of linear motion of an inertial mass which has been generally constrained to motion along a single axis but which is nonetheless affected by motion from all other directions. Hence, the signals generated by such transducers can be contaminated by signal components due to motion from all other directions.
As a result of recent advances in seismic reflection and refraction investigations of the earth, geophysicists and seismologists have begun to sense and record multiple components of the earth's response to seismic energy. Such investigations have employed two or more separate transducers, each generally responsive to ground motion along one axis, at each recording station or a single geophone having two or more spring-mounted inertial masses, wherein each inertial mass is generally responsive to the ground motion along one axis, at each recording location. Regardless of the nature of the transducers employed, the signals generated by such transducers can be contaminated by signal components due to ground motion from all directions.
Because of the recent advances in seismic reflection and refraction investigations in sensing and recording multiple components of the earth's response to generated seismic energy, it is highly desirable to obtain seismic signals which more truly represent the earth's response to the imparted seismic energy along selected axes. The multicomponent transducer of the present invention can develop one or more signals, each representative of a component of ground motion along a separate axis, from a single inertial mass which are more truly representative of the components of ground motion along such separate axes.